Chromium-tantalum alloys



United States Patent 3,138,456 CHRQMIUM-TANTALUM ALLOYS Alan R. Edwards, Surrey Hills, Victoria, Australia, assignor to Commonwealth of Australia, Canberra, Aus- However, the ability to be worked by extrusion, forging, rolling and like procedures is frequently required in a1- loys for turbine rotor blading and this ability is in general possessed by the alloys of the present invention.

It has been ascertained that alloys containing 0.5 to

5 g fi gaggg ?gfi fiafgfig ga ggf gg agzg 7% by weight of tantalum with the balance chromium Claims priority, application Australia Oct. 22, 1956 have satisfactory properties for the purpose of this in- 6 Cl i (CL 75-176) vention. The amount of tantalum in the alloys is preferably in the range 1 to 4%. At temperatures of 950 to This invention relates to chromium-tantalum alloys 10 1000 C. alloys within the range specified have shown and has for its object the provision of new alloys having minimum creep rates under stress which compare favourgood structural properties at high temperatures and parably with the creep rates under similar conditions of a ticularly suitable for such applications as high performhigh strength heat resistant alloy at present in commercial ance gas turbine rotor blading. use as shown in Table I which now follows:

Table I Stress Test Minimum Tertiary Alloy Condition (in tons/ Temperacreep rate creep sq. in.) ture (in./in./hr.) after C (hrs) Commercialhigh strength heatresistant alloy".-- Fullyheattreated g 5% Chromium, 1.5% tantalum Extruded 6 950 40 1 s 1 chromiumimtantalum iififhaiijjjjiiiiiiij 2 323 ltiit it 1 32 chromiumifimmlum --{%3Zsa1::::::::::::: 13 S28 it i l tl fi ffjj 1388 1 Test discontinued. No tertiary creep.

Alloys according to the invention are broadly char- The commercial alloy referred in the foregoing Table I acterized in that they consist essentially of 0.5 to 7% 30 i n alloy f Chromium, cobalt, titanium, by weight of tantalum, incidental ingredients and im- 2% aluminum and the balance nickel. The expression purities including gaseous impurities, iron and other Fully heat treated in the foregoing Table I means metals not exceeding a total of 0.5%, and the balance Solution treated 1150 C., and aged 700 C. chromium. The commercial alloy tested had a minimum creep The term incidental ingredients and impurities does -rate of approximately 1 10" /hr. under a stress of 6 not include the metals titanium, vanadium, niobium, tons/ sq. in. at a temperature of 815 C. so that the alloys molybdenum, aluminum silicon and mixtures thereof, of the invention provide an advance of up to 140 C. on which may be included as a further alloying component, the existing alloy. On a weight comparison, all the chroprovided that the chromium content should not be less mium-tantalum alloys of this invention are lighter than than 85%. the comparison alloy.

The lower limit of 85% of the chromium content has Alloys according to the invention can be hot-worked been found necessary to ensure that the alloys meet the at high temperatures while a proportion of the alloys following requirements for gas turbine rotor blading: can be cold worked at lower temperatures.

(a) An acceptably low density.The tensile stress on For hot-working, high speed extrusion is employed, rotor blading is directly proportional to the density of preferably using uncooled steel dies and a molten glass the alloy used, so that the accepted density for currently H lubricant. The alloy is heated for extrusion in a pro: used turbine alloys is substantially less than 9 grammes/ tective atmosphere of hydrogen or an inert gas, such as cc. To meet this requirement, alloys of chromium with argon or helium to minimize surface contamination by heavy metals must contain not less than 85% chromium. atmospheric gases, particularly nitrogen. This heating (b) Good resistance to high temperature oxidation. method is also used for hammer forging, which is con- The naturally high oxidation-resistance of chromium is P, ducted in the same temperature range. It is possible to seriously impaired if it is alloyed With a total of more produce a considerable range of shapes by hot-working. than 15% of poorly oxidation-resistant heavy metals. In particular, the extrusion method can be used to make (c) Acceptable hardness and machineability.-Alloys aerofoil sections, with or without thickened root secof chromium with heavy metals containing less than 85% tions, suitable for the production of turbine blades. chromium come into the category of hard metals, noted Thus it has been found possible to extrude the 2% for their resistance to wear and to machining operations. tantalum alloy at temperatures above 1200 C. starting It has, however, been ascertained that the alloys of the with a 1 /2" diameter arc-cast ingot and finishing with a present invention, containing not less than 85% chro- /2" diameter rod. Small arc-cast ingots containing up mium, can be readily machined with normal machine to 5% tantalum can be hammer-forged at temperatures tools. Since the alloys are required to be finished to the above 1200 C. to a useful extent using particular hanclose tolerances of turbine rotor blading, this easy madling techniques and one blow per heat. The main feachineability is an essential feature. ture of the handling techniques is the use of tongs and (d) F0rmabilz'ty.No high-strength alloy which conholders made of solid molybdenum. These usually resists preponderantly of chromium with the addition of main in contact with the chromium alloy ingots during heavy metals can be formed by the accepted metalworking operations unless it contains at least chromium.

the whole of the period of heating prior to forging, thus minimizing the heat loss which would otherwise occur Patented June 23, 1964' in transferring the ingots from the furnace to the hammer face.

The strength at high temperature of alloys according to the invention is such that cold-working must usually totalling not more than 0.5%, this total including gaseous impurities such as nitrogen and oxygen and non-gaseous impurities such as iron.

A high strength, heat-resistant alloy falling within the be conducted at temperatures well above room-temper- 5 scope of the present invention consists essentially of 0.5 ature, in the range 5001300 C. to 4% tantalum, 0.1 to 4% molybdenum, 0.1 to 1% Heat treatment, if employed, consists of an ageing niobium and 0.1 to 2% silicon, incidental impurities in treatment from 5 to 50 hours at the intended service temeluding gaseous impurities, iron and other metals not perature, or up to 200 C. above this temperature. The exceeding a total of 0.5%, and the balance chromium. normal range for this treatment is 900 C. to 1200 C. This application contains subject matter common to, and This may or may not be preceded by a high-temperais a continuation-in-part of my patent application Serial ture solution treatment in the range 1200 to 1600 C. No. 850,523, filed November 3, 1959, which latter appli- The alloys according to the invention may be used cation, in turn, was a continuation-in-part of my parent in the cast condition, or in the hot-worked or coldpatent application Serial No. 690,891, filed October 18, worked conditions, with or without heat-treatment. The 1957. Applications Serial Nos. 690,891 and 850,523 materials are intended primarily for the rotor and stator have since become abandoned. blading of gas turbine engines, and in other applications I claim; requiring high load-carrying ability at temperatures of 1. A high strength heat resistant alloy consisting essen- 900 C. and higher. tially of 0.5 to 7% by weight of tantalum, incidental in- The alloys can be shaped by normal machining methgredients and impurities including gaseous impurities and ods, using high-speed steel or carbide tools, or grindiron not exceeding a total of 0.5% and the balance chroing wheels with a copious supply of cutting lubricant. mi rn I addition to tantalum there may be included in the 2. A high strength heat resistant alloy consisting essenalloys from 0.1 to 7% of one or more of the following tially of 0.5 to 7% tantalum, 0.1 to 7% of a further alloyl m s titanium, Vanadium, niobium, molybdenum, 2 ing component selected from the group consisting aluminium and silicon. The partial substitution of one of titanium, vanadium, niobium, molybdenum, aluor more of these elements for the high-density main alminium, silicon and mixtures thereof, and the balance loying addition tantalum gives a desirable reduction i chromium and incidental impurities, the chromium conthe density of the alloys and it has been ascertained that tent amounting to not le than 85% by weight f th such substitution causes little or no detriment to the total alloy composition, and the impurities including gfinefal level of high temperature strength as shown gaseous impurities and iron not exceedingatotal of 0.5%. in Table II which now follows: 3. A high strength heat resistant alloy consisting essen- Table II Stress (in Test Tem- Minimum Tertiary Alloy Condition tonslsqin.) perature Creep rate creep (in C.)- (in./in./hr.) alter (hrs.)

Chromium, 3% tantalum, 0.2% titanium, 0.5% Cast 6 1,000 19.6 10- 330 Chi-ii iiiim, 2% tantalum, 0.1% titanium, 0.5% {Cast.... 6 1,000 13.2 106 1243 Silicon, Extruded. 6 1,000 51 10- 332 Chromium, 2% tantalum, 0.5% niobium, 0.5% Cast 6 1,000 4.i 1[)- 342 Cl ii' tiiiiiiim, 0.5% tantalum, 3% molybdenum, Cast 6 1,000 16X10' 248 0.5% titanium, 0.5% silicon.

I See footnote 1, Table I.

It has further been ascertained that titanium and nitially of 0.5 to 4% tantalum, 0.1 to 1% titanium and 0.1 obium enhance ductility and general handling qualities to 2% silicon, incidental impurities including gaseous imand that aluminium and silicon improve the already purities and iron not exceeding a total of 0.5%, and the high oxidation resistance of the alloys, as shown in Table balance chromium.

III which now follows: 4. A high strength heat resistant alloy consisting essen- Table I tially of 0.5 to 4% tantalum, 0.1 to 4% molybdenum, 0.1 to 1% titanium and 0.1 to 2% SlllCOl'l, incidental impurities including gaseous impurities and iron not ex- ,jig gi gg gffgg gigg ceeding a total of 0.5%, and the balance chromium. at 1.0006 micro- 5. A high strength heat resistant alloy consisting essen- Auoy Common grammes/sqcm) tially of 0.5 to 4% tantalum, 0.1 to 1% niobium and 0.1 to 2% silicon, incidental impurities including gaseous iza? impurities and iron not exceeding a total of 0.5%, and

the balance chromium. Commercial high strength heat Fully heat 604 1,080 6. A high strength heat resistant alloy consisting essenresistant alloy. treated. tially of 0.5 to 4% tantalum, 0.1 to 4% molybdenum, gEQEE' fggffi g- 832%:1: 2}? 0.1 to 1% niobium and 0.1 to 2% silicon, incidental imsilicon. 5 purities including gaseous impurities and iron not ex- *;{g$}g; tantalum 2% 410 ceeding a total of 0.5%, and the balance chromium.

The commercial alloy referred to in the foregoing Table References Clted m the file of this patent III is an alloy of the same composition as the commercial P UNITED STATES PATENTS alloy referred to in Table I. Th s IE ls p h 3,030,206 Buck Apr. 17, 1962 loys also contain not less than 85% by weig t of c romium. They retain the required properties of accept- OTHER REFERENCES able hardness, machineability and formability and thus Kubaschewski et al.: Journal of the Institute of Metals, have fully satisfactory properties for the purpose of this volume 75, 1949, pages 403 and 410-412. Published by invention. There may also be impurities in the alloys, the Institute, London, England. 

1. A HIGH STRENGTH HEAT RESISTANT ALLOY CONSISTING ESSENTIALLY OF 0.5 TO 7% BY WEIGHT OF TANTALUM, INCIDENTAL INGREDIENTS AND IMPURITIES INCLUDING GASEOUS IMPURITIES AND IRON NOT EXCEEDING A TOTAL OF 0.5% AND THE BALANCE CHROMIUM.
 2. A HIGH STRENGTH HEAT RESISTANT ALLOY CONSISTING ESSENTIALLY OF 0.5 TO 7% TANTALUM, 0.1 TO 7% OF A FURTHER ALLOYING COMPONENT SELECTED FROM THE GROUP CONSISTING OF TITANIUM, VANADIUM, NIOBIUM, MOLYBENUM, ALUMINIUM, SILICON AND MIXTURES THEREOF AND THE BALANCE CHROMIUM AND INCIDENTAL IMPURITIES, THE CHROMIUM CONTENT AMOUNTING TO NOT LESS THAN 85% BY WEIGHT OF THE TOTAL ALLOY COMPOSITION, AND THE IMPURITIES INCLUDING GASEOUS IMPURITIES AND IRON NOT EXCEEDING A TOTAL OF 0.5%. 